The semiconductor integrated circuit (IC) industry has experienced rapid growth in the past several decades. Technological advances in semiconductor materials and design have produced increasingly smaller and more complex circuits. These material and design advances have been made possible as the technologies related to processing and manufacturing have also undergone technical advances. As a size of the smallest component has decreased, numerous challenges have risen. For example, the need to perform higher resolution lithography processes grows. One lithography technique is extreme ultraviolet lithography (EUVL). Other techniques include X-Ray lithography, ion beam projection lithography, electron beam projection lithography, and multiple electron beam maskless lithography.
EUVL is a promising patterning technology for very small semiconductor technology nodes, such as the 14-nm technology node, and beyond. EUVL is very similar to optical lithography in that it needs a mask to print wafers, except that it employs light in the EUV region, i.e., at about 13.5 nm. At the wavelength of 13.5 nm, most materials are highly absorbing. Thus, reflective optics, rather than refractive optics, are used in EUVL. Although existing methods of EUVL have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. For example, challenges rise to improve the EUVL throughput, especially for low pattern density layers, such as a via layer, due to a relatively low transmittance through the vias. It is desired to have improvements in this area